The present invention relates generally to mechanical presses and in particular to a shutheight adjustment mechanism utilizing a hydraulic tie rod assembly to change press shutheight while the press is operating.
Mechanical presses, for example, stamping presses and drawing presses, comprise a frame having a crown and bed with a slide supported within the frame for motion toward and away from the bed. The slide is driven by a crankshaft having a connecting arm connected to the slide. Such mechanical presses are widely used for stamping and drawing operations and vary substantially in size and available tonnage depending upon the intended use.
In prior art presses of this type, the slide is generally connected to the crankshaft by a connection mechanism rod which is adjustable in length. The connecting rod is attached to another member that is adjustable in its relation to the slide so that the shutheight opening between the slide and the bed can be adjusted to accommodate various die sets. A normal slide adjustment mechanism adjusts the slide to a predetermined operating shutheight. Alternatively, the bed portion or bolster of the press may have its position adjusted relative to the slide so as to adjust the shutheight therebetween, as disclosed in U.S. Pat. No. 3,858,432. Regardless of the mode of shutheight adjustment, the slide is generally guided on the uprights of the press frame extending between the crown and the bed so that the parts of the die set remain in precise registration as the slide reciprocates.
A prior art patent, U.S. Pat. No. 4,502,379, shows a press in which shutheight is controlled by adjustment members located between the press crown and bed. Expansion and contraction of the adjustment members was accomplished by supplying hydraulic fluid into the members and thereby changing shutheight. This prior press has a disadvantage, in that by including the adjustment member within the press uprights, the cross section of the press uprights necessarily becomes larger. Another operational problem exists that if a seal on the adjustment member fails, the entire press would have to be dismantled to replace the seal.
Another example of press shutheight control is described in U.S Pat. No. 4,939,918, in which a fluid chamber beneath the lower press die is filled with pressurized oil to cause changes in press shutheight or load. A disadvantage to this system is that it does not lend itself to simple retrofitting on existing presses.
In mechanical presses utilized in stamping staked laminations, for example, there is a need to maintain shutheight tolerances to within 0.001 to 0.002 inches. Staked laminations are normally utilized in construction of the stator or rotor cores of electric motors. These laminations need precisely stamped surfaces to allow the laminations to be press fit together. Control of press shutheight is also necessary to maintain accurate part tolerances and prolong die life. A particular problem with punch presses is that the press shutheight normally varies with changes in press speed and thermal changes in the press itself.
The present invention is directed to fill the needs and overcome the aforementioned problems associated with mechanical press shutheight adjustment mechanisms wherein it is desired to accurately control shutheight while the press is in operation by controlling the connecting force on the press tie rods.